In Django's admin, you can add instance method calls to an edit page via the readonly option.
Can I do something similar with a ModelForm, and display the results of an instance method call? Preferably making it part of the forms visible_fields list.
My templates are quite generic so they are looping through the forms visible fields list and I would prefer not to alter these.
Oke, my solution will be quite hacky, but you could maybe do something like this:
class YourModelForm(forms.ModelForm):
class Meta:
model = YourModel
fields = []
def __init__(self, *args, *kwargs):
super(YourModelForm, self).__init__(*args, **kwargs)
# You can also user insert, to add on a certain position
self.visible_fields.append(self.instance.method())
Now a problem could be that you append a value, because I don't know how you render your fields. But you could fix this by append a Field-like object, which returns escaped (and saved) html on the necessary methods you call.
Other hacky option, add an additional field, set with an widget its attributes to disabled=disabled, and since a disabled input value isn't submitted with the form, set it required=False.
Related
I am pretty new to django and have a question. I got a ModelForm using Widgets. Since I have a field called discount which I only want to be editable if the displayed model fullfills some requirements, I make it read-only using a widget entry:
class Meta:
widgets = {'discount': forms.TextInput(attrs={'readonly': True})}
Now I want to make it possible to write to this field again, iff the Model (here called Order) has its field type set to integer value 0.
I tried to do so in the html template but failed.
So my next idea is to make the widget somehow dependent to the model it displays, so in kinda pseudocode:
class Meta:
widgets = {'discount': forms.TextInput(attrs={'readonly': currentModel.type == 0})}
Is there a proper way to do something like this?
Thanks in advance
You can overwrite __init__ of your model form class to modify the widget:
class MyModelForm(...):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs):
instance = kwargs['instance']
self.fields['discount'].widget.attrs['readonly'] = instance.type == 0
Might be worth noting that setting the widget to readonly does not prevent a malicious user to modify the field anyways. Make sure to properly validate on the server side.
Unless you define a model instance on the form creation, you have a generic model definition, not a model instance.
Looks like you may want to change the form behavior after user interaction, to do that you have to use a javascript.
I have a Django model with a Foreign key to a table that contains about 50,000 records. I am using the Django forms.ModelForm to create a form. The problem is I only need a small subset of the records from the table the Foreign key points to.
I am able to create that subset of choices in the init method. How can I prevent ModelForm from creating that initial set of choices?
I tried using the widgets parameter in the Meta method. But Django debug toolbar indicates the database is still being hit.
Thanks
The autogenerated ModelChoiceField will have its queryset initialized to the default. The widget is not where you are supposed to customize the queryset property.
Define the ModelChoiceField manually, initialize its queryset to be empty. Remember to name the ModelChoiceField the same as the one that would have been automatically generated, and remember to mention that field in the fields tuple. Now you can set the queryset from the constructor and avoid the database being hit twice.
If you are lucky (and you probably are, please test though), the queryset has not been evaluated during construction, and in that case, defining the ModelChoiceField manually is not required.
class YourModelForm(ModelForm):
your_fk_field_name = forms.ModelChoiceField(queryset=YourModel.objects.none())
class Meta:
model = YourModel
fields = ('your_fk_field_name', .......)
def __init__(self, *args, **kwargs):
super(YourModelForm, self).__init__(*args, **kwargs)
self.fields['your_fk_field_name'].queryset = ....
In a Django app, I'm having a model Bet which contains a ManyToMany relation with the User model of Django:
class Bet(models.Model):
...
participants = models.ManyToManyField(User)
User should be able to start new bets using a form. Until now, bets have exactly two participants, one of which is the user who creates the bet himself. That means in the form for the new bet you have to chose exactly one participant. The bet creator is added as participant upon saving of the form data.
I'm using a ModelForm for my NewBetForm:
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
widgets = {
'participants': forms.Select()
}
def save(self, user):
... # save user as participant
Notice the redefined widget for the participants field which makes sure you can only choose one participant.
However, this gives me a validation error:
Enter a list of values.
I'm not really sure where this comes from. If I look at the POST data in the developer tools, it seems to be exactly the same as if I use the default widget and choose only one participant. However, it seems like the to_python() method of the ManyToManyField has its problems with this data. At least there is no User object created if I enable the Select widget.
I know I could work around this problem by excluding the participants field from the form and define it myself but it would be a lot nicer if the ModelForm's capacities could still be used (after all, it's only a widget change). Maybe I could manipulate the passed data in some way if I knew how.
Can anyone tell me what the problem is exactly and if there is a good way to solve it?
Thanks in advance!
Edit
As suggested in the comments: the (relevant) code of the view.
def new_bet(request):
if request.method == 'POST':
form = NewBetForm(request.POST)
if form.is_valid():
form.save(request.user)
... # success message and redirect
else:
form = NewBetForm()
return render(request, 'bets/new.html', {'form': form})
After digging in the Django code, I can answer my own question.
The problem is that Django's ModelForm maps ManyToManyFields in the model to ModelMultipleChoiceFields of the form. This kind of form field expects the widget object to return a sequence from its value_from_datadict() method. The default widget for ModelMultipleChoiceField (which is SelectMultiple) overrides value_from_datadict() to return a list from the user supplied data. But if I use the Select widget, the default value_from_datadict() method of the superclass is used, which simply returns a string. ModelMultipleChoiceField doesn't like that at all, hence the validation error.
To solutions I could think of:
Overriding the value_from_datadict() of Select either via inheritance or some class decorator.
Handling the m2m field manually by creating a new form field and adjusting the save() method of the ModelForm to save its data in the m2m relation.
The seconds solution seems to be less verbose, so that's what I will be going with.
I don't mean to revive a resolved question but I was working a solution like this and thought I would share my code to help others.
In j0ker's answer he lists two methods to get this to work. I used method 1. In which I borrowed the 'value_from_datadict' method from the SelectMultiple widget.
forms.py
from django.utils.datastructures import MultiValueDict, MergeDict
class M2MSelect(forms.Select):
def value_from_datadict(self, data, files, name):
if isinstance(data, (MultiValueDict, MergeDict)):
return data.getlist(name)
return data.get(name, None)
class WindowsSubnetForm(forms.ModelForm):
port_group = forms.ModelMultipleChoiceField(widget=M2MSelect, required=True, queryset=PortGroup.objects.all())
class Meta:
model = Subnet
The problem is that ManyToMany is the wrong data type for this relationship.
In a sense, the bet itself is the many-to-many relationship. It makes no sense to have the participants as a manytomanyfield. What you need is two ForeignKeys, both to User: one for the creator, one for the other user ('acceptor'?)
You can modify the submitted value before (during) validation in Form.clean_field_name. You could use this method to wrap the select's single value in a list.
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
widgets = {
'participants': forms.Select()
}
def save(self, user):
... # save user as participant
def clean_participants(self):
data = self.cleaned_data['participants']
return [data]
I'm actually just guessing what the value proivded by the select looks like, so this might need a bit of tweaking, but I think it will work.
Here are the docs.
Inspired by #Ryan Currah I found this to be working out of the box:
class M2MSelect(forms.SelectMultiple):
def render(self, name, value, attrs=None, choices=()):
rendered = super(M2MSelect, self).render(name, value=value, attrs=attrs, choices=choices)
return rendered.replace(u'multiple="multiple"', u'')
The first one of the many to many is displayed and when saved only the selected value is left.
I found an easyer way to do this inspired by #Ryan Currah:
You just have to override "allow_multiple_selected" attribut from SelectMultiple class
class M2MSelect(forms.SelectMultiple):
allow_multiple_selected = False
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
participants = forms.ModelMultipleChoiceField(widget=M2MSelect, required=True, queryset=User.objects.all())
Is there an obvious way to convert a ModelForm into a regular Form without the instance setting logic?
I have an Update/Create ModelForm View I'd like to convert into a SearchView by using input from the exact same list of fields to query the model but it causes problems with required fields and types since the ModelForm attaches data to self.instance immediately.
I've ended up hacking into the metaclass to get what I want but I feel like I could easily be missing some solution right before my eyes overriding some function. I don't really enjoy pulling core django code...
Other forms of hackery would be preferable to copy and pasting the entire metaclass.
class ModelFormMetaclass(type):
def __new__(cls, name, bases, attrs):
formfield_callback = attrs.pop('formfield_callback', None)
try:
parents = [b for b in bases if issubclass(b, ModelToForm)] #<-- here
# ... rest of class
class ModelToForm(BaseForm):
__metaclass__ = ModelFormMetaclass
Update:
It appears ModelForm._post_clean() is responsible for instance construction / related field validation.
Currently I'm disabling _post_clean() and seeing where that takes me.
Given a model with ForeignKeyField (FKF) or ManyToManyField (MTMF) fields with a foreignkey to 'self' how can I prevent self (recursive) selection within the Django Admin (admin).
In short, it should be possible to prevent self (recursive) selection of a model instance in the admin. This applies when editing existing instances of a model, not creating new instances.
For example, take the following model for an article in a news app;
class Article(models.Model):
title = models.CharField(max_length=100)
slug = models.SlugField()
related_articles = models.ManyToManyField('self')
If there are 3 Article instances (title: a1-3), when editing an existing Article instance via the admin the related_articles field is represented by default by a html (multiple)select box which provides a list of ALL articles (Article.objects.all()). The user should only see and be able to select Article instances other than itself, e.g. When editing Article a1, related_articles available to select = a2, a3.
I can currently see 3 potential to ways to do this, in order of decreasing preference;
Provide a way to set the queryset providing available choices in the admin form field for the related_articles (via an exclude query filter, e.g. Article.objects.filter(~Q(id__iexact=self.id)) to exclude the current instance being edited from the list of related_articles a user can see and select from. Creation/setting of the queryset to use could occur within the constructor (__init__) of a custom Article ModelForm, or, via some kind of dynamic limit_choices_to Model option. This would require a way to grab the instance being edited to use for filtering.
Override the save_model function of the Article Model or ModelAdmin class to check for and remove itself from the related_articles before saving the instance. This still means that admin users can see and select all articles including the instance being edited (for existing articles).
Filter out self references when required for use outside the admin, e.g. templates.
The ideal solution (1) is currently possible to do via custom model forms outside of the admin as it's possible to pass in a filtered queryset variable for the instance being edited to the model form constructor. Question is, can you get at the Article instance, i.e. 'self' being edited the admin before the form is created to do the same thing.
It could be I am going about this the wrong way, but if your allowed to define a FKF / MTMF to the same model then there should be a way to have the admin - do the right thing - and prevent a user from selecting itself by excluding it in the list of available choices.
Note: Solution 2 and 3 are possible to do now and are provided to try and avoid getting these as answers, ideally i'd like to get an answer to solution 1.
Carl is correct, here's a cut and paste code sample that would go in admin.py
I find navigating the Django relationships can be tricky if you don't have a solid grasp, and a living example can be worth 1000 time more than a "go read this" (not that you don't need to understand what is happening).
class MyForm(forms.ModelForm):
class Meta:
model = MyModel
def __init__(self, *args, **kwargs):
super(MyForm, self).__init__(*args, **kwargs)
self.fields['myManyToManyField'].queryset = MyModel.objects.exclude(
id__exact=self.instance.id)
You can use a custom ModelForm in the admin (by setting the "form" attribute of your ModelAdmin subclass). So you do it the same way in the admin as you would anywhere else.
You can also override the get_form method of the ModelAdmin like so:
def get_form(self, request, obj=None, **kwargs):
"""
Modify the fields in the form that are self-referential by
removing self instance from queryset
"""
form = super().get_form(request, obj=None, **kwargs)
# obj won't exist yet for create page
if obj:
# Finds fieldnames of related fields whose model is self
rmself_fields = [f.name for f in self.model._meta.get_fields() if (
f.concrete and f.is_relation and f.related_model is self.model)]
for fieldname in rmself_fields:
form.base_fields[fieldname]._queryset =
form.base_fields[fieldname]._queryset.exclude(id=obj.id)
return form
Note that this is a on-size-fits-all solution that automatically finds self-referencing model fields and removes self from all of them :-)
I like the solution of checking at save() time:
def save(self, *args, **kwargs):
# call full_clean() that in turn will call clean()
self.full_clean()
return super().save(*args, **kwargs)
def clean(self):
obj = self
parents = set()
while obj is not None:
if obj in parents:
raise ValidationError('Loop error', code='infinite_loop')
parents.add(obj)
obj = obj.parent